1. Field of the Invention
The present invention relates to a wavelength selective switch.
2. Description of the Related Art
As an example of a conventional N×1 wavelength selective switch, a wavelength selective switch 500 of 5×1 used in FIG. 35 and FIG. 36 is available. FIG. 35 is a side view showing a structure of the conventional wavelength selective switch 500, and FIG. 36 is a top view showing the structure of the conventional wavelength selective switch 500. In this case, N is an integer greater than 1.
The wavelength selective switch 500 includes input ports 510a, 510b, 510c, and 510d (hereinafter, ‘input ports 501a to 501d’), an output port 510e, a lens array 530, a first lens 540, a second lens 550, a dispersive element 560, a third lens 570, and a plurality of mirrors 590a, 590b, 590c, 590d, and 590e (hereinafter, ‘mirrors 590a to 590e’). In the wavelength selective switch 500, light which is wavelength-multiplexed is input from an arbitrary input port from among the input ports 510a to 510d, and light of an arbitrary wavelength is selected from wavelengths separated by the dispersive element 560, and is output to the output port 510e. In FIG. 35 and FIG. 36, wavelength-multiplexed light of the input port 510a is shown to be output to the output port 510e. 
It is desirable that the number of ports of a wavelength selective switch is increased, and when the number of ports is increased in the N×1 wavelength selective switch, for connecting an arbitrary input port to an output port, there is a need to increase a deflection angle of each mirror in the mirror array. However, there is a restriction on the deflection angle of the mirror, and the number of input ports to be connected to the output port is determined by this restriction. In 1×N wavelength selective switch, the number of output ports to be connected to the input port is determined by the deflection angle of a mirror similarly as in a case of N×1 wavelength selective switch.
Therefore, in the conventional N×1 wavelength selective switch or the 1×N wavelength selective switch, for increasing the number of ports, the number of input ports which are to be connected to the output port and the number of output ports which are to be connected to the input ports are increased by connecting in multiple stages, a plurality of independent M×1 wavelength selective switches or a plurality of 1×M wavelength selective switches. FIG. 37 is a block diagram showing a structure of a 10×1 wavelength selective switch 600 of an ADD type, and FIG. 38 is a block diagram showing a structure of a 1×10 wavelength selective switch 800 of a DROP type. In the 10×1 wavelength selective switch 600 shown in FIG. 37, the number of ports is increased by connecting three 5×1 wavelength selective switches 500 in three stages. Moreover, in the 1×10 wavelength selective switch 800 shown in FIG. 38, the number of ports is increased by connecting three 1×5 wavelength selective switches 700 in multiple stages.
However, as it has been mentioned above, in the conventional N×1 wavelength selective switch and the 1×N wavelength selective switch, since the plurality of M×1 wavelength selective switches and the plurality of 1×M wavelength selective switches are arranged to be connected in multiple stages for increasing the number of ports, a plurality of members of the wavelength selective switch to be arranged in M×1 or 1×M is necessary in manufacturing thereof. Moreover, assembly man-hours for that many numbers of members is necessary, thereby leading to an increase in a necessary cost of an overall apparatus. Moreover, in addition to the increased cost, when the apparatus is structured in multiple stages, an overall size of the apparatus becomes large, and there is an increase in weight of the apparatus.